1. Field of the Invention
This invention relates to improvements in trucks for railroad locomotives and cars and, more particularly, to improved pedestal liners that form bearing surfaces for those portions of the trucks that are slidably engaged to enable the wheels and body of the locomotive car to move relative to each other in a generally vertical direction. More particularly, this invention relates to an improved pedestal liner that is not secured to the pedestal leg, but instead is permitted to "float" relative both to the pedestal leg and the journal box.
2. Description of the Prior Art
The truck upon which a railroad locomotive or car body is supported is comprised essentially of two side frames tied together by a transverse piece called the "bolster." One type of truck commonly used for locomotives is referred to as a "pedestal truck". The pedestals are part of the side frames and are formed in inverted "U"-shaped sections that horizontally position and hold the journal box while permitting the journal box to move essentially vertically in relationship to the truck. The two projections that comprise the "U" of the pedestal are called the .music-flat.pedestal legs" and the space between them the "jaw". The jaw is closed at the bottom when the journal box is inserted by means of a pedestal tie bar. In this arrangement, the journal box is held positioned in vertical sliding relationship with the truck and, since the locomotive body is supported by the bolster and side frames, vertical movement between the locomotive body and the journal box, journal and wheels is permitted.
As considerable wear takes place at the engaging faces of the pedestal and the journal box, it is common practice to attach wear plates to both the pedestal legs and the journal boxes. The former are referred to as "pedestal liners" and the latter as "journal box wear plates." Conventionally, the journal box wear plate is attached to the journal box by welding, whereas the pedestal liner is removably mounted as by bolting onto the pedestal legs.
Until recent years, the wear plates conventionally have been manufactured of hardened high-carbon spring steel or other alloy steel such as magnesium steel. More recently, however, it has been found that more satisfactory performance can be obtained utilizing wear plates made from some of the tougher plastics such as nylons, polyacetals, polyurethanes, polyolefins, polycarbonates, polyesters, rigid polyvinyls, polyethers, polysulfones, polyimides, polyamidimides, polysilcones, and the like. As is disclosed in U.S. Pat. No. 3,554,618, these plastic materials may be used to form a generally "U"-shaped wear plate that can be bolted onto the pedestal leg of a railroad truck.
Plastic pedestal liners gained almost immediate acceptance throughout the industry due to the fact that they outwear alloy steel liners and thus require less frequent replacement. Further, they are advantageous in that they reduce the wear on the journal box wear plate. This is of considerable advantage since when the wear plate on the journal box becomes unduly worn, the welds must be broken and a new plate welded in its place.
While plastic pedestal liners have, by and large, proven considerably more satisfactory in use than the steel alloy liners, they do sometimes fail by cracking at those points where they are bolted onto the pedestal. It is believed that under conditions of heavy use, stress crazing may embrittle the plastic and cause it to break at the bolts where it is secured to the pedestal leg.
It has been conventional to bolt the pedestal liner to the pedestal leg and, indeed, it has always been thought necessary to do so, particularly with respect to steel pedestal liners. If the steel liners are not fastened to the pedestal leg, either by bolting or by welding, they tend to wear the mating cast steel pedestal legs rapidly, which then have to be rebuilt or replaced; if not secured, the liners may hang up, with resulting damage to liners and mating parts; and they will, if not secured, cause pounding and fatigue on the journal boxes, and further may cause excessive noise from loose parts in metal-to-metal contact.